Chapter 5 - Section 5.3 - Special Products - Exercise Set - Page 367: 33

$25-49x^2$

Using $(a+b)(a-b)=a^2-b^2$ or the special product of the sum and difference of like terms, the product of the given expression, $ (5-7x)(5+7x) ,$ is \begin{array}{l}\require{cancel} 5(5)-7x(7x) \\\\= 25-49x^2 .\end{array}